1. Field of the Invention
The present invention relates to a strain sensor using an inductor, and in particular, to a strain sensor that measures strain by detecting the amount of deformation of a conductor caused by stress.
2. Description of the Related Art
The inventor of the present application has proposed a “position sensor” (Jpn. Ptn. Appln. KOKAI Publication No. 2002-81902) in which a soft magnetic film is formed on a back surface of a conductor provided on an object to be sensed to enable sensitivity to be improved and enable a decrease in sensitivity to be suppressed even when the distance between the conductor and an inductor increases.
If the above-mentioned position sensor is applied to a strain sensor, the sensitivity of this strain sensor is not sufficient if it must detect very slight deformation of the conductor and soft magnetic film. Thus, it is impossible to ensure a high signal/noise (S/N) ratio sufficient for signal processing executed by a succeeding circuit.
As an example of a strain sensor, Jpn. Pat. Appln. KOKAI Publication No. 2000-292294 discloses a method of detecting a change in the internal pressure of a closed container having an upper bottom portion and a lower bottom portion, using a strain sensor formed on an upper bottom plate or a lower bottom plate constituting the upper bottom portion or the lower bottom portion, respectively. However, this strain sensor has at least one coil formed of a magnetic thin film having magnetic strain, the coil being provided in a central portion of a non-magnetic material plate via a dielectric layer. Thus, this conventional sensor is based on an operational principle different from that of the sensor according to the above proposal which has a conductive coil disposed away from an object being detected.